To examine the internal consistency and validity of the Infant-Toddler Social and Emotional Assessment (ITSEA) and Brief-ITSEA (BITSEA) parent-report questionnaires in an early intervention sample. A sociodemographically diverse sample of 192 parents of 11- to 36-month-old children referred to early intervention programs completed surveys containing the ITSEA, BITSEA, and Child Behavior Checklist (CBCL). Parents were interviewed with the Vineland Adaptive Behavior Scales. Evaluators blind to children's status on the ITSEA and BITSEA rated child behavior during developmental assessments. Finally, a subsample of 71 children was administered the Mullen Scales of Early Learning. Findings support the internal consistency of the ITSEA and BITSEA, with the majority of Cronbach's alphas above .70. Supporting validity, ITSEA and BITSEA problem scores correlated significantly with CBCL Internalizing and Externalizing scores (rs=.28 to .78), as well as with observational ratings of problem behaviors on constructs paralleling the ITSEA domains (rs=.21 to .45). In contrast, ITSEA Competence and BITSEA Competence demonstrated moderate negative associations with CBCL scores (rs=−.39 to −.43). Finally, ITSEA Competence and BITSEA Competence correlated significantly with developmental level on the Mullen, Vineland Socialization, and observational ratings of competence (rs=.25 to .43). Emphasizing the importance of addressing social-emotional issues in early intervention settings, 58.6% of children had high social-emotional/behavioral problems and/or low competence on the ITSEA; 39.8% had high ITSEA Problems and 38.5% had low ITSEA Competence. Results indicate the need to assess social-emotional adjustment in early intervention settings and support the use of the ITSEA and BITSEA for this purpose.